A service-level agreement (SLA) is a part of a service contract where the level of service is formally defined. As an example, internet service providers can include service level agreements within the terms of their contracts with customers to define the level(s) of service being sold. In this case the SLA will typically have a technical definition in terms of mean time between failures (MTBF), mean time to repair or mean time to recovery (MTTR), various data rates, throughput, jitter, or similar measurable details.
In an Ethernet Virtual Circuit environment, the enforcement of bandwidth quotas as part of a Service Level Agreement requires administrative efforts to propagate the settings into the devices enforcing the SLA. Adding a new device responsible to verify and enforce the SLA typically requires administrative and management steps before the SLA can be monitored and enforced.
In order for a device to enforce SLA settings, the actual Committed Information Rate (CIR) and the Excess Information Rate (EIR) must be explicitly defined. CIR is the average bandwidth for a virtual circuit guaranteed by an internet service provider to work under normal conditions. At any given time, the bandwidth should not fall below this committed figure. The bandwidth is usually expressed in kilobits per second (kbit/s). Above the CIR, an allowance of burstable bandwidth is often given, whose value can be expressed in terms of additional rate, known as the EIR. The provider guarantees that the connection will always support the CIR rate, and sometimes the EIR rate provided that there is adequate bandwidth. The Peak Information Rate (PIR), which is the CIR plus excess burst rate (EIR), is either equal to or less than the speed of the access port into the network.
When inserting a new device (such as a Network Interface Device or NID) in an existing network to verify and enforce the SLA settings, it is usually required to propagate the CIR and EIR values, adding to the management burden and possibly creating a potential for discrepancies when the CIR and EIR need to be updated for many different devices, each with their respective management interfaces.
The RFC 2544 standard, established by the Internet Engineering Task Force (IETF) standards body, is the de facto methodology that outlines the tests required to measure and prove performance criteria for carrier Ethernet networks. The standard provides an out-of-service benchmarking methodology to evaluate the performance of network devices using throughput, loopback, frame loss and latency tests, with each test validating a specific part of an SLA. The methodology defines the frame size, test duration and number of test iterations. Once completed, these tests provide performance metrics of the Ethernet network under test.
RFC 2544 and other similar standards aimed at detecting a packet loss situation, gradually increase the amount of synthetic traffic generated until a packet loss is detected. This process may take a significant amount of time for each Ethernet Virtual Circuit (EVC) being tested. Packet loss occurs when one or more packets of data travelling across a computer network fail to reach their destination. Packet loss is distinguished as one of the three main error types encountered in digital communications.